1. Field of the Invention
The present invention relates to a digital signal recording and reproducing apparatus for digitally recording and reproducing digital audio and video signals, and also methods therefor.
2. Description of the Prior Art
Recently, developments on the digital video recorder (digital VCR) has been made to record the video and audio signals in digital format which provides high quality and stable image in comparison to analog video recorder even after the tape dubbing or editing. Digital video recorders with rotational head of D1 and D2 types are now available for the business use, and the digital video recorders for the home use are now on the way by the recent technology development, such as image compression technology.
The digital video recorders for the home use has one problem in the density of the recording data per unit area of the tape. For the home use, the recording density on the tape should be set higher than those for the business use so that the home users will not be suffering from using many cassette tapes to record one program. Also the size of the cassette should be maintained at a reasonable size to enable them to be kept in cabinets in ordinary houses.
The increase of the amount of tape to record a program in home uses digital VCR will result in decrease of practical use. Therefore, for the home use digital VCR, a technology called high efficiency coding is used to remove the redundancy in the video signal and eventually reducing the amount of data for recording, thus reducing the amount of tape necessary to record a program. Furthermore, in the digital VCR, error correction codings, such as parity check codes, are added to the video and audio signals to correct errors during the data reproducing. Adding of the error correction codings results in increase of the data to be recorded. Therefore, the removal of the redundancy in the video signal is one of the most important tasks to enable the recording of inevitable data, such as the error correction codings.
The digital video recorder has been described in detail in a report "19-mm type D-1 cassette-tape record" March 1986, SMPTE J., 95,3 or in a report "The Composite Digital Format and its Applications" October 1987, SMPTE J., 96, 10.
In a conventional business use digital video recorder, a synchronization pattern, ID, and a 4-byte fixed pattern are recorded immediately before the signal recording area as a mini-synchronization block, and only the synchronization pattern and ID are recorded immediately after the signal area. When signal detection is in three synchronization block units, there are only two opportunities to detect the first synchronization block of the signal area when there is one mini-synchronization block immediately before the signal area. Compared with the second and subsequent synchronization blocks for which there are three detection opportunities, the fewer detection opportunities provided for the first synchronization block means there is a high probability that detection will not be possible. As a result, AV signals demodulated from the reproduced signal will be missing the audio or visual information contained in the undetected block, resulting in lower image or sound quality. In addition, the 4-byte fixed pattern data provides no meaningful information to the recorded data, and yet increases the amount of data that must be recorded.
This is particularly problematic in consumer digital VCRs due to the increased operating cost resulting from increased tape consumption, which also results in larger cassettes and creates additional cassette storage problems. It follows that increased tape consumption significantly impairs the practical commercial benefits of the digital VCR. This has led to the use of so-called bit-rate reduction technologies to reduce tape consumption by eliminating redundant components from the video signal and thereby reduce the amount of information recorded. To correct for errors during data reproduction in digital VCRs, an error correction code is added to the recorded audio and video signals. This error correction code, however, also increases the amount of recorded data, thus further increasing tape consumption. It is therefore essential to minimize data redundancy in the recorded signal in order to record the error correction code and other essential data and also prevent further increasing total tape consumption.
However, because the track width and other added information is small relative to the AV signal data, it is not possible to generate identical synchronization blocks. This makes it necessary to record the information to an area separate from the AV data. This, however, increases the amount of recorded information, and increases tape consumption.
Furthermore, to distinguish this added information from the AV signal area, the synchronization blocks must have a synchronization pattern different from that of the AV signal area, and separate dedicated circuits are required for playback processing. This further increases the circuit size and cost. These problems are major impediments to widespread acceptance of consumer digital VCRs.